Cage mill

ABSTRACT

The present invention relates to a cage mill for comminuting material and is particularly concerned with a cage mill having a plurality of counter-rotating cages with the cages widening in the radially outward direction and having hard facing applied to the leading faces of the impact bars and to the axially inner faces of the support rings at the ends of the impact bars.

United States Patent Stephenson et al.

[54] CAGE MILL [72] Inventors: Earle W. Stephenson, Latrobe, Pa.; James G. Newberry, Lakeland, Fla.; Robert C. l-lazzard, Mt. Vernon, Ind.

[73] Assignees: International Minerals & Chemlcal Corporation, by said Newberry and said Hazzard; Kennametal lnc., Latrobe, Pa. by said Stephenson [22] Filed: Aug. 6, 1969 [21] AppLNo; 847,929

[52] U.S.Cl. ..241/l87, 241/188 A, 241/197 [51] lnt.Cl. [58] Field ofSearch ..241/188,188.5,l97, 187

[56] References Cited UNITED STATES PATENTS 250,125 11/1881 Bennett ..241/188.5 X 2,534,301 12/1950 Sennholtz.. 2,628,038 2/1953 Rogers ..24l/197 X 51 May 2,1972

2,867,387 l/l959 Dodds ..24l/275 3,503,561 3/1970 Johnson... ....24l/188 2,155,150 4/1939 Schacht ...24l/187 X 3,047,243 7/1962 Meger et al. ..24l/l88 R FOREIGN PATENTS OR APPLICATION S 42,255 1/1888 Germany ..241/188.5 158,227 8/1954 Australia ..24l/188 R 699,460 1 H1940 Germany ..24 1/197 Primary Examiner-Andrew R. J uhasz Assistant Examiner-Michael Koczo, Jr. Allorney-Melvin A. Crosby [57] ABSTRACT The present invention relates to a cage mill for comminuting material and is particularly concerned with a cage mill having a plurality of counter-rotating cages with the cages widening in the radially outward direction and having hard facing applied to the leading faces of the impact bars and to the axially inner faces of the support rings at the ends of the impact bars.

13 Claims, 9 Drawing Figures Patented May 2, 1972 4 SheetsSheet l INVENTORS Ui W, STEPHENSON NEWBGRQY c. unzzalw Patented May 2, 1972 4 Sheets-Sheet 2 IN VENTOR5 J 6. uewasnav ROGER! C, HA R Patented May 2, 1972 4 Sheets-Sheet 4 INVENTORS ERQLE w. sTsvuzufioel JHMES G. "EWGERQY BY R 659; C, HRZZARD CAGE MILL The present invention also relates to cage mills whereinthe flow path of material through the mill is modified from what is conventional to produce superior results and to protect the mill and is particularly concerned with a construction for cage mills in which the portion of the cage mill which are normally abraded during operations of the mill are protected by wear resistant facings.

Cage mills are, of course, known and are employed for reducing material passed therethrough in size. For example, certain ores are advantageously treated to reduce the particle size thereof for further treatment, as by liquid agents, or to pennit the material to be handled in slurry form or the like. Coal, and the like, is also reduced to pulvurent form for burning in certain types of burners.

Many devices are employed for effecting such reduction in particle size including rod mills, hammer mills, ball mills, and impact mills but a particular advantageous type of device for work of this nature is a cage mill. A cage mill consists of one or more cages consisting of axially spaced rim parts with circumferentially spaced bar elements extending axially therebetween. When more than one cage is used, the cages are concentric and alternate ones of the cages revolve in respectively opposite directions. The present invention is concerned with a cage mill having a plurality of cages. Material to be reduced in size is fed into the inside of the smallest cage and will then move outwardly through the cages, being impacted by the axial bars of the respective cages and thereby reduced in size. A housing surrounds the outermost cage and the reduced material is thus confined and is discharged from the housing to any desired receiver.

While such cage mills are known and have been widely used, they have nevertheless been effective, with respect to rapid abrasion, particularly when used for the treatment of certain materials, namely, materials which are highly abrasive. Abrasive materials can create such rapid wear on cage mills that the use of such a mill becomes uneconomical. Furthermore, a cage mill which becomes abraded is dangerous because of the possibility of breaking of the weakened cages.

The lack of economy can arise, in particular, in connection with an integrated process wherein material enters the process at one point and flows continuously therethrough to another point and wherein the process involves apparatus including a cage mill. In such a case, if the cage mill becomes ineffective, or fails, due to abrasion of the cages thereof, so that it must be shut down for reconditioning, the entire process will also be shut down. Shut downs of this nature, if occurring at more than a certain minimum frequency, can represent the difference between profitable and unprofitable operation of the process. Abrasion of cages occurs not only on the bars thereof but also on the structural parts of the cages that support the bars. The bars can be made of a wear resistant material but the structural parts are usually made of steel and can abrade away quite rapidly under certain circumstances.

With the foregoing in mind, it is a primary objective of the present invention to provide a cage mill construction in which deterioration of both the impact bars and structural parts of the cages, due to abrasion, is greatly reduced thereby permitting longer periods of operation of the cage mill before servicing thereof is required.

Another object of the present invention is the provision of abrasion resistant facing for theworking parts of a cage mill so applied as fully to protect the cage mill parts while at the same time permitting readily replacement of the abrasion resistant material.

Still another object of the present invention is the provision of a cage mill of the nature referred to so modified in construction as to produce superior results with respect to the reduction in size of material passed through the cage mill.

It is also an object of this invention to provide a cage mill construction in which the basic structural components of the cage mill can be made extremely strong and wherein the said components are so arranged as to permit abrasion resistant members to be replaceably mounted thereon in such a manner as substantially completely to protect the portions of the cage mill which would normally be abraded during operation of the cage mill.

Another object of the present invention is the provision of a cage mill construction in which the material passing through the mill is caused to flow along a path such that no parts of the mill, particularly, structural parts, which are not easily accessible are abraded by this material.

The foregoing objects as well as still other objects and advantages of the present invention will become more apparent upon reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a cage mill adapted to embody the features of the present invention;

FIG. 2 is a vertical sectional view taken on about line lI-II of FIG. I and showing the several cages of the mill in cross section; I

FIG. 3 is a sectional view indicated by line Ill-III on FIG. 2 showing the cages in cross section;

FIG. 4 is a fragmentary view showing an end member more in detail;

FIG. 5 is a section indicated by line V-V on FIG. 2 and showing how a typical axial bar extending between the end rings of a cage is provided with abrasion resistant protection;

FIG. 6 is a sectional view indicated by line VIVI on FIG.

FIG. 7 is a sectional view showing the connection of a cross bar ofa cage to an end ring of the cage;

FIG. 8 is a perspective view showing how the facing is applied to the protective member for a cross bar of a cage; and

FIG. 9 is a section on line lX-IX of FIG. 3 showing how the protective members are mounted on the end rings of the cages.

BRIEF SUMMARY OF THE INVENTION The present invention relates to a cage mill having counter rotating cages therein each of which consists of end members or end rings with axial bars extending between the end members or end rings and secured thereto, as by welding. The cages are constructed of steel and the steel of the cages is protected against abrasion, in the regions thereof which are subjected to abrasion in use, by specially constructed protective members detachably mounted on the end members or end rings and on the axial bars. These protective members consist of steel backing with hard wear-resistant facing thereon.

The hard wear-resistant facing is preferably a cemented carbide composition, such as cemented tungsten carbide. The facing material referred to, particularly cemented tungsten carbide, is extremely resistant to abrasion and will last many times as long as the best steel under the same conditions of abrasion.

The hard carbide material is, however, extremely expensive and has certain drawbacks as a basic structural material and is, therefore, supported on a steel backing and presented to the material passing through the mill in such a manner that the carbide is subjected principally to abrasion and to impact by the material passing through the mill and is not loaded structurally as in torsion or tension. Furthermore, the protective members are made relatively small for ease of manufacture and installation and the carbide applied thereto is in the form of segments so that there is little tendency for the carbide to fail due to deflection of any of the parts of the cages and which deflection could impose stresses on the carbide material tending to break it if the carbide pieces were too large.

DETAILED DESCRIPTION Referring to the drawings somewhat more in detail, as will be seen in FIG. 1, a cage mill according to the present invention may comprise a base 10 having bearing support platforms l2 upstanding therefrom and on which are mounted the bearings 16 for the drive shafts of the mill. The drive shafts, of which there are two, extend out opposite sides of the mill and have drive pulleys mounted thereon which are belted to the pulleys of one or more electric drive motors. The mill comprises a housing 18 mounted on base and within which are cages which are mounted on the drive shafts. Housing 18 can advantageously discharge downwardly as indicated by arrow 20 in FIG. 1 while the feed for the mill can be in the form of a vertical supply chute 22 which, at its lower end, has an inclined portion 24 that directs the incoming material to the inside of the innermost one of the cages.

Turning now to FIG, 2, it will be seen that the cage mill has a first drive shaft 26 extending therein from one side and a second drive shaft 28, coaxial with shaft 26, extending therein from the other side. Each drive shaft drives two of the four counter rotating cages in the mill. For example, drive shaft 26 has mounted thereon a hub 27 which has connected thereto a relatively heavy disc like member 30 just inside the one wall of housing 18 of the mill. Near its outer periphery disc like plate 30 has fixed thereto, as by welding, or integral therewith, an end member or end ring 32. Fixed to ring 32 in circumferentially spaced relation and extending axially therefrom are bars 34. Bars 34, at the ends opposite ring 32, are connected to a second end member or ring 36. In FIG. 2 only one bar is shown for each cage but it will be understood that the bars in each cage are disposed at regular intervals about the circumference of the cage at intervals of about 20 to 30 with the smaller intervals occurring in the larger diameter cages. The outermost cage thus might have 18 bars and the innermost cage might have only 12 bars.

Disc like plate 30, inwardly from end ring 32, has attached thereto a relatively short cylindrical member 40 which extending axially inwardly. At its axially inner end cylinder 40 carries, or has integral therewith, a ring or end member 42 for the cage second inwardly from the outermost cage. Ring 42, similarly to ring 32, has axial bars 44 fixed thereto and extending axially in the mill and secured at their opposite ends to another ring or end member 46.

It will be seen that the cage made up of bars 34 and the end members 32 and 36 connected thereto, and the cage consisting of the bars 44 and the end members 42 and 46 connected thereto, rotate in the same direction as a unit because of the rigid connection therebetween by cylindrical member 40 and disc like plate 30.

The other drive shaft 28 has mounted thereon a hub 29 which has fixed thereto another relatively heavy disc like plate 48 which is adjacent plate 30 but smaller in diameter. Near its outer periphery plate 48 carries, or has integral therewith, end member or ring 50 to which is fixed one end of each of a plurality of circumferentially distributed bars 52. Bars 52 extend axially in the mill and at their other ends are connected to a second end member or ring 54.

Ring 54 has fixed thereto, or integral therewith, an annular plate 56 to the radially outer region of which is fixed, or integral, another end member or ring 58. Bars 60 have their one ends fixed to ring 58 and are distributed circumferentially in the mill and have their other ends fixed to still another end member or ring 62.

The cage consisting of bars 52 and end rings 50 and 54, and the cage consisting of bars 60 and end rings 58 and 62, rotate as a unit, and in a direction opposite to the other cages of the mill. The shafts 26 and 28 are driven in respectively opposite directions and at a speed of about 500 to 600 revolutions per minute.

In the mill illustrated, the outer cage might have, for example, an average radius of about 26 inches and the innermost cage might have an average radius of about 12 inches. There might be a gap of about 1 inch or slightly less between the inner periphery of one cage and the outer periphery of the cage disposed next inwardly therefrom. In length, bars 34 might be a little less than 18 inches long, bars 52 might be about inches long, bars 44 could be a little over l2 inches long, and bars 60 a little over 9 inches long. A mill constructed to about the sizes mentioned above could handle about 200 tons per hour of, for example, a phosphate bearing ore with the cages rotating at the speed referred to, namely, about 500 to 600 RPM and with a total power input to the two shafts of about 300 to 350 horsepower.

The particular proportions given for the lengths of the bars of the cages and the approximate diameters of the cages provides for a fan shaped flow of material through the mill at a divergent angle substantially in excess of the angles of divergence heretofore employed in cage mills. Cage mills have been constructed in which the material fans out somewhat as it moves radially outwardly through the cages, as in US. Pat. No. 2,033,757, but this comes about as an incident to the construction of the mill and does not provide for a flow path which fans out to the degree contemplated herein. It has been found that proportions about like those indicated above, and which provide for a substantially wider angle of divergence than has heretofore been employed, from about 15 to 30 included angle, produce superior results with respect to reduction of the material passing through the mill.

Furthermore, the flow pattern of the material passing through the mill is such that the wear resistant facing applied to the mill can be confined to certain specific working regions thereof and regions adjacent thereto, while other parts of the mill are so disposed out of the flow path of the material that facing need not be applied thereto. The merit of so arranging the mill to provide for the described widely diverging flow path of material therethrough will be evident because the minimum amount of the extremely expensive and heavy wear resistant facing material is required while, at the same time, those regions of the mill which must be provided with the hard facing are so located that the detachable hard faced protective members can be formed to relatively simple configurations and the regions to be protected are so disposed that easy access thereto can be had.

Referring now to FIGS. 2 and 3, it will be seen that the end rings 32 and 36 of the outermost cage are protected by attaching thereto in end to end relation, the curved steel parts on the left side of FIG. 2, and 72 on the right side of FIG. 2. Each steel part is channel-shaped in cross section and is notched at the trailing end to accommodate one of the axial bars 34. Each steel part is provided with a stud 74 near the leading end which extends through the pertaining end ring to receive a nut to hold the protective member in place.

The channel-shaped steel parts 70 and 72 are faced with relatively thin pieces of carbide which may be brazed to the steel part or secured thereto by an epoxy cement. The steel parts 70 and 72 applied to the rings 32 and 36 have carbide pieces 76 applied to the legs thereof which face toward the axial center of the respective cage and smaller pieces of carbide at 78 which are applied to the shorter legs of the respective channel-shaped steel parts and which face radially inwardly and outwardly of the cage.

The axially and radially facing sides of end rings 32 and 36 are thus protected against abrasion by protective. members which can readily be replaced merely by removing one nut and removing the protective member. It will be appreciated that each protective member locates at the trailing end on one of the axial bars 34 and, at its other end, is held in place on the pertaining end ring by a single stud welded to the longer leg of the steel part on the side opposite the carbide facing and extending through a hole provided therefor in the respective end ring.

The trailing end of each of the curved protective members on the end rings is, as mentioned, in overlapping relation with the protective members on the bars of the cages. This is taken advantage of by placing in each end ring member an adjusting member in the form of a screw which abuts the curved protective member on the side thereof toward the pertaining end ring so that after the protective members have been placed on the bars of the cage, the adjusting member 75 can be drawn up to push the trailing ends of the curved protective members axially toward each other and thereby take up any gaps that might exist between the curved protective members on the bars and between the protective members on the bars when there are more than one of these members employed.

For a given cage, the adjustable members 75 can be positioned in one end ring only and this is adequate for closing all of the gaps between the protective members on the respective cage. Each adjustable member 75, after being adjusted, is locked in place by a nut 75'.

The end rings of the cages inwardly from the outermost cage are protected by similar channel-shaped protective members. A typical one of such protective members is illustrated in FIG. 4 wherein it will be seen that steel part 73 is shaped so as to fit about the respective end ring 50. The radially outer leg of steel part 73 has carbide pieces 71 thereon, the axially inner side of steel part 73 has carbide pieces 77 thereon, and the radially inner leg of the steel part has carbide pieces 79 thereon.

As to the axial bars of the several cages these are protected by protective members of the nature shown in FIG. 5. All of the bars have the same cross sectional shape and all of the protective members for the bars also have the same cross sectional shape. It has been found that a mill having the cages of the relative axial length shown in FIG. 2 can have the bars faced by protective members made up of members of only two basic lengths. A typical member is shown in FIG. 8. Each of the protective members for the bars, as will be seen in FIG. 5, comprises a steel body 80 adapted for mounting on the leading side of the respective bar with the leading face of the steel body inclined slightly backwardly from a radius. The radially inner side of the steel body inclines outwardly toward the rear. Each steel body 80 has two or more threaded holes 82 therein for receiving the screws 84 which secure the steel body parts to their respective bars.

The radially inner side of each body part 80 has the cemented carbide facing 86 applied thereto. The radially outer side has the cemented carbide facing 88 applied thereto, while the leading face has carbide facing 90. The leading face of the member is subjected to greater wear than the inner and outer faces and carbide facing 90 is, therefore, substantially thicker than the facing 86 and 88.

The inner forward corner of steel body 80 is notched and bar like carbide facing 92 is applied thereto. It will be appreciated that the protective members applied to the bars of the cages completely protect the bars against abrasion but, at the same time, the protective members can readily be replaced and are so constructed as to observe the maximum in economy in respect to the quantity of the heavy, expensive carbide employed for protective purposes.

The protective members for the bars of the cages are made in two lengths. The shorter one of the protective members for the bars, has single pieces of carbide on each of its three faces whereas the longer one of the members, has several pieces of carbide on each face arranged thereon in end to end relation. The shorter protective member is about 2.65 inches in length and the longer member is about 8.3 inches in length. The protective members for the several bars of the inner cage is made up by placing a single one of the longer members on each of the bars 52 of the smallest cage while on the second cage outwardly, having the bars 44, each bar carries one of the longer members and one of the shorter members. The third cage outwardly, consisting of the bars 60, has one of the longer members and two of the shorter members mounted on each bar, and the bars 34 of the outermost cage each have two of the longer members mounted thereon.

It will be noted, upon reference to FIG. 5, that there is a substantial region of each of the arcuate protective members on the end rings covered in the region radially outwardly and inwardly and forwardly of the bars of the respective cage by the protective members placed on the bars. By so arranging the protective members to overlap at the ends of the bars, abrasion of the bars and end rings of the cages at these points is prevented.

From the foregoing it will be appreciated that a mill constructed according to the present invention has all of the parts thereof subjected to abrasion fully protected at all times. The mill thus remains in active operative service for a much greater length of time than would be the case even with the best steel components subjected to the abrasive influence of the material passing through the mill.

Furthermore, with the extremely wide angle of divergence of the path of the material passing through the mill, superior results are obtained and the mill will process large quantities of material in the shortest possible time with the most uniform results. It appears that, as the material is impacted by each bar and breaks and tends to fan out, the bars of the next cage, by being of such length that the material is permitted to fan out relatively freely, will contact the maximum percentage of the material and thereby effect uniform and rapid reduction in size of the particles of the material. A smaller angle of divergence of the flow path introduces the possibility that the particles of the material will crowd together and will be less completely impacted by the bars, or hammers, of the mill and in which case less uniform reduction in size will be had and the capacity of the mill will be correspondingly reduced.

While the carbide faced protective members referred to withstand most of the abrasion that is encountered in the mill, it may be of advantage to provide other portions of the mill with protective members of a material substantially less expensive than cemented carbides. Thus, in FIG. 2, hard steel protective members are shown at 95 and 97 on the outer corner ofa cage member. This type of facing is relatively inexpensive and can be applied to any region of the mill that might be subjected to mild abrasion during operation of the mill. Other steel members of this nature are shown at 99, I01, and 103 in FIG. 2.

Similarly, with respect to the disc like supporting plate for the innermost cage, a wear resistant carbide facing at 99 might be applied by gas or electrodeposition using rods of the facing material. This type of protective facing could be applied to substantially any part of the mill subjected to relatively mild abrasion.

Still further, shaft 28 and hub 29 thereon on the side facing the inside of the inner most cage might have a latex or rubber like coating 100 applied thereto. Any other protective measures for portions of the mill can be resorted to because all of the regions of the mill subjected to a high degree of abrasion or protected by the carbide faced protective members according to the present invention.

In one application of the cage mill according to the present invention, phosphorus bearing ore at about 15 mesh is fed into the mill and the output from the mill will be about mesh minimum size. The yield from the ore is substantially increased by the reduction in the ore particle size and at relatively low cost. The ore has a high silica content but the carbide lining according to the present invention prevents rapid deterioration of the mill.

In other instances the size of the particles fed into the mill can be substantially larger, up to an inch or more.

Modifications can be made in the structure illustrated within the scope ofthe appended claims.

What is claimed is:

1. In a cage mill having a housing with concentric counter rotating cage means therein and means to introduce material to be comminuted into the innermost one of said cage means for radially outwardly movement thereof through the cage means during operation of the mill; each said cage means comprising axially spaced end ring portions and substantially rectangular bars extending axially between and fixed to said end ring portions in circumferentially spaced parallel relation and having the longer cross sectional dimensions thereof disposed generally radially, hard wear resistant protective members mounted on the axially inner sides of said end ring portions and on the forwardly facing sides of said bars, means detachably connecting said protective members to said bars and rings, said protective members comprising steel supports and hard cemented metal carbide facing secured to each said support and covering the region thereof which is exposed to the material passing through the mill, said protective members comprising arcuate first members on each said end ring portion and straight second members on each said bar, said first members extending between adjacent bars of the respective cage means and also extending radially both outwardly and inwardly beyond the said bars and including notch means in at least one end thereof embracing the adjacent bars, the axially outermost ends of said second members on said bars abutting the axially inner side of at least one end of the said first members adjacent the bar.

2. A cage mill according to claim I in which said second members abut the notched ends of said first members, said means connecting said first members to said end ring portions being spaced circumferentially from the region of abutment of said second members with said first members, and adjustable abutment means on each said end ring portion engaging the axially outer side of each said first member at a point therealong between said notched end thereof and the means connecting the respective first member to the pertaining end ring portion.

3. A cage mill according to claim 2 in which said notched ends of said first members are the trailing ends thereof.

4. A cage mill according to claim I in which the said notch means in said first members are at one end thereof only, the other ends of said first members being free of notches and abutting the adjacent bars, said means connecting said first members to said end ring portions being located near the said other ends of said first members, and means for pressing said other ends of said first members axially inwardly into firm abutting engagement with the adjacent ends of said second members.

5. A cage mill according to claim 1 in which the said carbide facing on each said member is in the form of a plurality of pieces of carbide distributed over the surface of the respective support in abutting side by side relation.

6. A cage mill according to claim 5 in which said carbide pieces on at least said second members differ in thickness from each other with the thicker pieces being located in the regions of greatest abrasion.

7. A cage mill according to claim 1 in which the central axial planes of said cage means are substantially coplanar, the bars of said cage means being progressively longer from the radially innermost cage means to the radially outermost thereof, the said end ring portions of each cage means being disposed axially outwardly from the end ring portions of the cage means next adjacent thereto on the radially inner side.

8. A cage mill according to claim 7 in which the widening of said cage means in the outwardly direction substantially corresponds to the widening of the flow path of the material passing through the cage mill due to the impacting of the material against the axial bars of the cage means whereby substantially the entire region of said cage means which is subjected to abrasion is confined to the exposed regions of the said second members on the said axial bars of the cage means.

9. A cage mill according to claim 1 in which the support for each said second member is substantially U-shaped so as to nest over the respective bar from the leading side thereof, the leading face of each said second member being substantially radial with respect to the pertaining cage means, the radially outer face of each said second member extending substantially at right angles to the leading face thereof, and the radially inner face thereof forming an included angle of less than with said leading face.

10. A cage mill according to claim 9 in which the corner of the steel support for each said second member at the radially inner edge of the leading face is notched, and said carbide facing on each said second member comprising at least one bar like piece of substantial cross section disposed in said notch and projecting outwardly therefrom both forwardly and inwardly from said support, said facing comprising other carbide pieces thinner than said bar like piece and extending therefrom along the leading face of said support and along the radially inner side of said support.

11. A cage mill according to claim 10 which includes at least one further carbide piece thinner than said bar like piece extending over the radially outer face of said steel support.

12. A cage mill according to claim 8 in which the included angle of the flow path of material through said cage means in the radially outward direction as confined by said end ring portions is on the order of about 15 to about 60 13. A cage mill according to claim 10 in which the radial distance between the radially outermost portion of the said second members of one cage means from the radially innermost portions of the said second members on the next larger cage means is on the order of about one-half the radial extent of each said second member.

i k i 

1. In a cage mill having a housing with concentric counter rotating cage means therein and means to introduce material to be comminuted into the innermost one of said cage means for radially outwardly movement thereof through the cage means during operation of the mill; each said cage means comprising axially spaced end ring portions and substantially rectangular bars extending axially between and fixed to said end ring portions in circumferentially spaced parallel relation and having the longer cross sectional dimensions thereof disposed generally radially, hard wear resistant protective members mounted on the axially inner sides of said end ring portions and on the forwardly facing sides of said bars, means detachably connecting said protective members to said bars and rings, said protective members comprising steel supports and hard cemented metal carbide facing secured to each said support and covering the region thereof which is exposed to the material passing through the mill, said protective members comprising arcuate first members on each said end ring portion and straight second members on each said bar, said first members extending between adjacent bars of the respective cage means and also extending radially both outwardly and inwardly beyond the said bars and including notch means in at least one end thereof embracing the adjacent bars, the axially outermost ends of said second members on said bars abutting the axially inner side of at least one end of the said first members adjacent the bar.
 2. A cage mill according to claim 1 in which said second members abut the notched ends of said first members, said means connecting said first members to said end ring portions being spaced circumferentially from the region of abutment of said second members with said first members, and adjustable abutment means on each said end ring portion engaging the axially outer side of each said first member at a point therealong between said notched end thereof and the means connecting the respective first member to the pertaining end ring portion.
 3. A cage mill according to claim 2 in which said notched ends of said first members are the trailing ends thereof.
 4. A cage mill according to claim 1 in which the said notch means in said first members are at one end thereof only, the other ends of said first members being free of notches and abutting the adjacent bars, said means connecting said first members to said end ring portions being located near the said other ends of sAid first members, and means for pressing said other ends of said first members axially inwardly into firm abutting engagement with the adjacent ends of said second members.
 5. A cage mill according to claim 1 in which the said carbide facing on each said member is in the form of a plurality of pieces of carbide distributed over the surface of the respective support in abutting side by side relation.
 6. A cage mill according to claim 5 in which said carbide pieces on at least said second members differ in thickness from each other with the thicker pieces being located in the regions of greatest abrasion.
 7. A cage mill according to claim 1 in which the central axial planes of said cage means are substantially coplanar, the bars of said cage means being progressively longer from the radially innermost cage means to the radially outermost thereof, the said end ring portions of each cage means being disposed axially outwardly from the end ring portions of the cage means next adjacent thereto on the radially inner side.
 8. A cage mill according to claim 7 in which the widening of said cage means in the outwardly direction substantially corresponds to the widening of the flow path of the material passing through the cage mill due to the impacting of the material against the axial bars of the cage means whereby substantially the entire region of said cage means which is subjected to abrasion is confined to the exposed regions of the said second members on the said axial bars of the cage means.
 9. A cage mill according to claim 1 in which the support for each said second member is substantially U-shaped so as to nest over the respective bar from the leading side thereof, the leading face of each said second member being substantially radial with respect to the pertaining cage means, the radially outer face of each said second member extending substantially at right angles to the leading face thereof, and the radially inner face thereof forming an included angle of less than 90* with said leading face.
 10. A cage mill according to claim 9 in which the corner of the steel support for each said second member at the radially inner edge of the leading face is notched, and said carbide facing on each said second member comprising at least one bar like piece of substantial cross section disposed in said notch and projecting outwardly therefrom both forwardly and inwardly from said support, said facing comprising other carbide pieces thinner than said bar like piece and extending therefrom along the leading face of said support and along the radially inner side of said support.
 11. A cage mill according to claim 10 which includes at least one further carbide piece thinner than said bar like piece extending over the radially outer face of said steel support.
 12. A cage mill according to claim 8 in which the included angle of the flow path of material through said cage means in the radially outward direction as confined by said end ring portions is on the order of about 15* to about 60* .
 13. A cage mill according to claim 10 in which the radial distance between the radially outermost portion of the said second members of one cage means from the radially innermost portions of the said second members on the next larger cage means is on the order of about one-half the radial extent of each said second member. 